1. Field of the Invention
The invention relates to detecting very low level emanations such as luminescence and fluorescence in the presence of sunlight.
2. Description of the Prior Art
Some biological colonies, such as phytoplankton, spontaneously emit low level luminescence, and most organic compounds generate distinctive low level fluorescence when illuminated by solar radiation. Such emanations are useful in sensing bioligical activity or the presence of specific organic compounds. The sunlight is, however, generally so bright that such low level emanations are masked thereby, rendering it impossible to detect and analyze the luminescence or fluorescence from a remote sensor in daylight without special instrumentation.
The prior art instrumentation utilized to perform observations of such low level emanations utilizes the principle of Fraunhofer line discrimination to remotely sense luminescent organisms and fluorescent organic compounds. Such instrumentation is predicated on the phenomenon that solar radiation exhibits dark lines in the spectrum thereof caused by selective absorption of radiation by the elements in the solar atmosphere. These lines are denoted as Fraunhofer lines. Within the dark Fraunhofer lines, little or no radiation from the sun arrives at the earth. Low level luminescence and fluorescence is observed in daylight by utilizing a very narrow passband filter to effect observations within the bandwidth of a Fraunhofer line. Since the Fraunhofer line discrimination instrumentation utilizes such a narrow band filter to perform the desired observation, such instruments are limited to observing only one spectral line of approximately 0.2 Angstrom units wide per sensor. Such filters inherently function only for light incident in a very narrow angular field, thus severely limiting the field of view of such remote sensors.